Shaped articles such as fibers and films of cellulose esters produced by the extrusion of a cellulose ester production solution are well known. Cellulose esters are produced from a cellulosic feedstock such as wood pulp or cotton linters. The cellulose ester is precipitated after acetylation and hydrolysis, is then washed and dried, and then redissolved in cellulose ester solvents such as aqueous acetone, or methylene chloride/alcohol. This solution is then filtered to form a production solution. The shaped articles are then produced from this production solution or extrudable solution by solvent evaporation techniques such as dry spinning to form fibers.
High production speeds are very desirable in that more shaped product can be formed during a set period of time than at lower production speeds. This is particularly important for the production of cellulose acetate fiber from a cellulose acetate/acetone dope solution by the dry spinning technique. Spinning speeds seem to be limited by the residence time required to remove the solvent from the wet filaments through diffusion and evaporation, and by reduced strength of the spinline while large quantities of solvent are present. Spinning speeds are also limited by the presence of non-uninformities in the dope such as particles, rheological inhomogeneities etc. which interact with the bulk rheological properties of the dope and with the spinning conditions. Spinning speeds can be increased by incorporating appropriate additives or diluents to drop the viscosity of the cellulose acetate/acetone solution. For example U.S. Pat. No. 3,272,638 discloses the addition of sugar to the spinning solution to increase the spinning rate, and U.S. Pat. No. 4,418,026 discloses the addition of poly(ethylene) glycol to the spinning solution to improve the spinnability. The methods of increasing the dry spinning spinnability of cellulose acetate/acetone solution by changing the viscosity of the spinning solution is limited by the thread spinline or threadline strength of the spinning medium. U.S. Pat. No. 3,952,081 discloses an alternative method of increasing the spinning speed of cellulose acetate fibers that entails partially avoiding the dry spinning process by extruding a solution of cellulose acetate at elevated temperature and at elevated pressure precipitating out insoluble cellulose acetate to form the cellulose acetate filamentary material. Although this method may improve the spinning speed, different equipment would be needed since dry spinning at mild conditions is the current method of producing cellulose acetate fibers.
It would be very desirable to be able to further increase the production speed of cellulose ester shaped articles by solvent evaporation techniques at mild conditions. It would be particularly desirable to be able to increase the dry spinning speed of a cellulose ester fiber beyond the speeds currently available limited by the current spinline strength.